Peak-to-Average-Power Reduction for OFDM Multiple Access

ABSTRACT

An Orthogonal Frequency Division Multiplexing (OFDM) transmitter generates OFDM multiple-access signals with low Peak-to-Average-Power Ratio (PAPR). A code-division multiplexer arranges original data symbols from different data streams inside each length-N symbol block, which is spread by a Discrete Fourier Transform (DFT) spreader. The arrangement of the original data symbols configures the DFT spreader to spread each original data symbol into a predetermined spread-DFT code division multiple access channel. The resulting DFT-spread data symbols are mapped to OFDM subcarriers, and an inverse discrete Fourier transform (IDFT) operates on the DFT-spread data symbols to generate an OFDM transmission signal having low PAPR.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.16/779,657, filed Feb. 2, 2020, which is a Continuation of U.S. patentapplication Ser. No. 15/988,898, filed May 24, 2018, now U.S. Pat. No.10,637,705, which claims priority to Provisional Appl. No. 62/510,987,filed May 25, 2017; and Provisional Appl. No. 62/527,603, filed Jun. 30,2017; and Provisional Appl. No. 62/536,955, filed Jul. 25, 2017; all ofwhich are hereby incorporated by reference in their entireties and allof which this application claims priority under at least 35 U.S.C. 120and/or any other applicable provision in Title 35 of the United StatesCode.

BACKGROUND I. Field

The present invention relates generally to wireless communicationnetworks, and more specifically to Peak-to-Average Power reduction ofmulticarrier waveforms.

II. Background

The background description includes information that may be useful inunderstanding the present inventive subject matter. It is not anadmission that any of the information provided herein is prior art orrelevant to the presently claimed inventive subject matter, or that anypublication, specifically or implicitly referenced, is prior art.

In multi-user communications, orthogonal frequency division multipleaccess (OFDMA) offers flexible resource allocation (subcarrierallocations to users) and scheduling. Dynamic allocation can furtherimprove performance compared to fixed allocation. For these reasons,OFDMA has been adopted as the downlink in LTE.

However, OFDMA suffers from high peak-to-average power ratio (PAPR)because the modulated subcarriers for different users combine randomlyto produce a signal with highly variable amplitude. This requires RFpower amplifiers (PAs) to operate with large back-offs (i.e.,transmitter PAs are made to operate at low efficiency operating pointsto ensure linearity). This trade-off is acceptable in sparse deploymentsof large base stations.

In dense LTE deployments, base stations are more power constrained, asdense deployments demand radio terminals that are significantly lessexpensive and operate at lower power. As LTE adopts fixed and mobilerelays, the network infrastructure will rely on autonomously powered(e.g., solar-powered) and battery-powered devices for downlink support.This will further drive the need for improvements in power-efficientdownlink signaling.

Similarly, user devices can be tasked with relaying WWAN radiotransmissions. In some aspects, user devices can cooperate, such as totransmit OFDM multiple-access signals in the uplink. For at least thesereasons, improvements to PAPR-reduction in both the uplink and downlinksignaling are needed. Peer-to-peer communications between user devicesand communications between clusters of user devices are also envisioned.Thus, there is a need for improvements to OFDM multiple access thatreduce PAPR while providing for flexible resource allocation andscheduling.

SUMMARY

In accordance with some aspects of the disclosure, these needs areremedied. Aspects disclosed herein can be configured for downlink,uplink, relay links, peer-to-peer links, as well as other communicationlinks across any network topologies.

In the downlink (e.g., at least one base station transmitting to one ormore terminals), some literature states that multiple access reduces tomultiplexing. However, other literature refers to downlink multiplexingof different user channels as multiple access. For example, in the 3GPPLong-Term Evolution (LTE) fourth-generation mobile broadband standard,the downlink is commonly described as orthogonal frequency-divisionmultiple access (OFDMA), which is the multi-user version of OFDM.Multiple access is typically achieved in OFDMA by assigning subsets ofthe subcarriers to individual users. Aspects of the disclosure thatprovide for downlink transmissions wherein a plurality of user channelsare combined over a shared medium is referred to as multiplexing.However, in view of the literature, such aspects can also be qualifiedas multiple access.

As an alternative to the downlink scheme in LTE, some aspects of thedisclosure provide for multicarrier code division multiplexing, whereinuser data from each of a plurality of UEs is spread by employing DFTspreading to produce a plurality of spread data symbols. The spread datasymbols are then carried over different OFDM subcarrier frequencies.

Specifically, whereas the OFDMA scheme in LTE assigns a differentsubcarrier set to each UE, aspects of the disclosure provide fortransmitting data to a plurality of UEs by using the same subcarriers.Aspects of the disclosure can employ code division multiplexing wherebyeach UE channel is provided with a different code set. This enables theuse of DFT spreading on the downlink in a manner that producessubstantial PAPR reduction of the transmission signal. Specifically,since the UEs share all N subcarriers instead of being assigned subsets(e.g., N₂, . . . , N_(K); where N=N₁+N₂+ . . . +N_(K)) of thesubcarriers, DFT spreading can be performed as a single N-pointspreading operation across the N subcarriers to yield lower PAPR than ifseparate spreading operations are performed across the subsets and thencombined.

In aspects of the disclosure, the spread user signals on the downlinkcan be easily synchronized, and all signals on one subcarrier experiencethe same radio channel properties. In such cases, an exemplaryimplementation maps different UE user data (and optionally, controlsignal data) to a symbol block of length-N. The mapping to specificpositions in the block provides for code-set assignment. The block isinput to an N-point FFT to generate spread data symbols, which aremapped to input bins of an IFFT. The IFFT may be an oversampling IFFT(e.g., an M-point IFFT, where M>N).

While the addition of the DFT spreading in the downlink transmitterrequires a corresponding de-spreader in the UE receiver, there are somecompelling advantages that can justify the added complexity. First, thespreading improves performance in the radio-access channel. Theperformance gain represents a larger budget for a combination ofbenefits, including reduced receiver power, improved error rate, supportfor higher modulation order, increased range, and more reliablecoverage. Secondly, since each user employs the full set of subcarrierfrequencies instead of a subset, the resulting diversity gain furtherimproves the performance in the radio-access channel. Third, a codewordin a downlink DFT-spread signal provides finer information granularitythan the LTE resource block. This can enhance overall network bandwidthefficiencies. Additional advantages and benefits can be realized for theaspects disclosed herein.

In one aspect, a base transceiver station (BTS) configured to providedownlink data transmissions to a plurality of user devices in a radioaccess network comprises a code-division multiplexer configured tomultiplex a plurality of user data streams into a set of symbol blocks.A DFT pre-coder coupled to the multiplexer spreads each symbol blockwith a set of spreading codes comprising coefficients of a DFT togenerate a plurality of spread data symbols. An OFDM transmittermodulates the plurality of spread data symbols onto a plurality ofdownlink OFDM subcarrier frequencies for transmission.

Aspects disclosed herein can be implemented as apparatus configurationscomprising structural features that perform the functions, algorithms,and methods described herein. Flow charts and descriptions disclosedherein can embody instructions, such as in software residing on anon-transitory computer-readable medium, configured to operate aprocessor (or multiple processors). Flow charts and functionaldescriptions, including apparatus diagrams, can embody methods foroperating a communication network(s), coordinating operations whichsupport communications in a network(s), operating network components(such as client devices, server-side devices, relays, and/or supportingdevices), and assembling components of an apparatus configured toperform the functions disclosed herein.

Groupings of alternative elements or aspect of the disclosed subjectmatter disclosed herein are not to be construed as limitations. Eachgroup member can be referred to and claimed individually or in anycombination with other members of the group or other elements foundherein. One or more members of a group can be included in, or deletedfrom, a group for reasons of convenience and/or patentability. When anysuch inclusion or deletion occurs, the specification is herein deemed tocontain the group as modified, thus fulfilling the written descriptionof all Markush groups used in the appended claims.

All methods described herein can be performed in any suitable orderunless otherwise indicated herein or otherwise clearly contradicted bycontext. The use of any and all examples, or exemplary language (e.g.,“such as”) provided with respect to certain embodiments herein isintended merely to better illuminate the inventive subject matter anddoes not pose a limitation on the scope of the inventive subject matterotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe inventive subject matter.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the invention willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the invention as set forthherein.

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All of the references disclosed herein all are incorporated by referencein their entireties.

BRIEF DESCRIPTION OF DRAWINGS

Flow charts depicting disclosed methods comprise “processing blocks” or“steps” may represent computer software instructions or groups ofinstructions. Alternatively, the processing blocks or steps mayrepresent steps performed by functionally equivalent circuits, such as adigital signal processor or an application specific integrated circuit(ASIC). The flow diagrams do not depict the syntax of any particularprogramming language. Rather, the flow diagrams illustrate thefunctional information one of ordinary skill in the art requires tofabricate circuits or to generate computer software to perform theprocessing required in accordance with the present disclosure. It shouldbe noted that many routine program elements, such as initialization ofloops and variables and the use of temporary variables are not shown. Itwill be appreciated by those of ordinary skill in the art that unlessotherwise indicated herein, the particular sequence of steps describedis illustrative only and can be varied. Unless otherwise stated, thesteps described below are unordered, meaning that the steps can beperformed in any convenient or desirable order.

FIG. 1 is a block diagram of a radio communication system in whichexemplary aspects of the disclosure can be implemented. Aspects of thedisclosure are not limited to the depicted system design, as suchaspects can be implemented in alternative systems, systemconfigurations, and applications.

FIG. 2A is a block diagram of a transmitter apparatus according toaspects of the disclosure.

FIG. 2B is a block diagram of a DFT spreader (such as can be employed asspreader 202 shown in FIG. 2A) in accordance with some aspects of thedisclosure. At least some of the blocks shown herein, such as in FIGS.2A and 2B can be implemented by special-purpose processors and/orgeneral-purpose processors programmed to perform functions disclosedherein.

FIG. 3A is a block diagram of a receiver apparatus according to aspectsof the disclosure.

FIG. 3B is a block diagram that depicts a portion of a receiver, such asa receiver that may be employed in a UE.

FIG. 4A is a flow diagram for a method performed in a radio transceiver,which can employ single-carrier frequency division multiple access(SC-FDMA) to produce a multiple-access OFDM transmission signal withreduced PAPR.

FIG. 4B is a flow diagram for a method that can be employed inaccordance with various aspects of the disclosure, such as forprocessing received spread-OFDM signals. In one aspect, for example, themethod depicted in FIG. 4B can be performed by a user equipment (UE) ora relay operating on received downlink signals.

FIG. 5 is a flow diagram that illustrates a method that can be used forgenerating a downlink shared channel (DL-SCH) transmission in accordancewith aspects of the disclosure.

FIG. 6 is a flow diagram that illustrates a method that can be used forprocessing a received DL-SCH transmission in accordance with aspects ofthe disclosure.

FIG. 7 depicts a set of modules, each comprising instructions stored ona non-transitory computer-readable memory and configured to instruct atleast one general-purpose processor (such as a processor core, a server,a distributed computing system, a Cloud computing system etc.) toperform functions disclosed herein.

FIG. 8 depicts a set of modules, each comprising instructions stored ona non-transitory computer-readable memory and configured to instruct atleast one general-purpose processor (such as a processor core, a server,a distributed computing system, a Cloud computing system, etc.) toperform functions disclosed herein.

FIG. 9 is a diagram that depicts a radio transmitter configured inaccordance with aspects of the disclosure.

FIG. 10 is a diagram that depicts a radio transmitter configured inaccordance with aspects of the disclosure.

FIG. 11 is a diagram that depicts a radio transmitter configured inaccordance with aspects of the disclosure.

FIG. 12 is a diagram that depicts a radio transmitter configured inaccordance with aspects of the disclosure.

FIG. 13 is a block diagram that illustrates components of a radiotransmitter according to some aspects of the disclosure.

FIG. 14 is a flow diagram that depicts the function of a spatialprecoder, such as the spatial precoder 1302.1-1302.N, according to someaspects of the disclosure.

DETAILED DESCRIPTION

Various aspects of the disclosure are described below. It should beapparent that the teachings herein may be embodied in a wide variety offorms and that any specific structure, function, or both being disclosedherein are merely representative. Based on the teachings herein oneskilled in the art should appreciate that an aspect disclosed herein maybe implemented independently of any other aspects and that two or moreof these aspects may be combined in various ways. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, such an apparatusmay be implemented or such a method may be practiced using otherstructure, functionality, or structure and functionality in addition toor other than one or more of the aspects set forth herein.

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the invention. It should be understood, however, thatthe particular aspects shown and described herein are not intended tolimit the invention to any particular form, but rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe scope of the invention as defined by the claims.

FIG. 1 is a block diagram of a communication network in which aspects ofthe disclosure can be implemented. A plurality N of geographicallydistributed base transceiver stations (BTSs) 101.1-101.N (BTS(1),BTS(2), . . . , BTS(N)) are communicatively coupled to at least onecentral processing system 111 via a communication network 105. Each BTS101.1-101.N comprises an antenna system configured for communicatingwith one or more mobile units (e.g., User Equipments, or UEs)120.1-120.K via a WWAN radio access network (RAN).

In one aspect, the first base transceiver station 101.1 comprises afirst antenna array comprising a first plurality M₁ of antennas102.1-102.M₁, the second base transceiver station 101.2 comprises asecond antenna array comprising a second plurality M₂ of antennas102.1-102.M₁, and the N^(th) base transceiver station 101.N comprises anN^(th) antenna array comprising an N^(th) plurality M_(N) of antennas104.1-104.M_(N). The base transceiver stations 101.1-101.N areconfigured to provide RAN services to a plurality K of mobile units120.1, 120.2, . . . , 120.K, each having its own antenna system 121.1,121.2, . . . , 121.K, respectively. Each antenna system 121.1, 121.2, .. . , 121.K comprises one or more antennas.

The communication network 105 can comprise a fiber network, a cable(e.g., “wired”) network, a wireless network (including a free-spaceoptical network), or any combination thereof. In some aspects, thenetwork 105 is referred to as a “fronthaul” network. In some aspects,the network 105 can comprise a backhaul network. In accordance with oneaspect of the disclosure, a network that connects base transceiverstations to a processing system configured to perform joint processing(e.g., system 111) can be referred to as a fronthaul, and a network(such as network 115) that connects processing elements of theprocessing system 111 can be referred to as a backhaul.

The terms “backhaul” and “fronthaul” can be used interchangeably in someaspects of the disclosure. A fronthaul is similar to a backhaul, which,at its simplest, links a radio access network to a wired (e.g., cable oroptical fiber) network. A fronthaul can comprise a backhaul, or aportion of a backhaul. For example, a fronthaul can comprise aconnection between one or more centralized controllers and remotestand-alone radio heads. A fronthaul can connect a central processor tomultiple base transceiver stations. A fronthaul connects multiple basetransceiver stations together when one or more of the base transceiverstations functions as a central processor. As used herein, a fronthaulmay comprise a traditional backhaul network. For example, a fronthaulcan comprise at least a portion of S1 and/or X2 interfaces. A fronthaulmay be part of a base station network.

In dense BTS deployments, some of the RAN processing can be distributedclose to the edge of the RAN edge, such as in the BTSs and/or in hubsthat connect BTSs together. Some processing can be performed fartheraway from the RAN edge, such as closer to and/or within a core network.In some aspects, RAN processing that is sensitive to latency isperformed at or near the RAN edge, such as in BTSs 101.1-101.N, whereasprocessing that is not as sensitive to latency can be performed fartheraway from the RAN edge, such as central processor 110 and/or adistributed computing system in a data center.

In one aspect of the disclosure, the RAN processing system 111 comprisesa distributed computing system configured to coordinate a plurality ofphysical processors (which may be centrally located or geographicallydistributed), such as to perform joint processing. In some aspects, theplurality of physical processors can be represented as processors111.1-111.N. In other aspects, virtual processors (such as virtual basestations implemented as software-defined radios (SDRs)) can berepresented as processors 111.1-111.N.

By way of example, but without limitation, physical processors in adistributed computing environment can be represented as processors111.1-111.N. As used herein, the term “processor” can refer to acomputer processor, a computer, a server, a central processing unit(CPU), a core, a microprocessor, and/or other terminology that indicateselectronic circuitry configurable for carrying out instructions of acomputer program. In some aspects, a processor comprises geographicallydistributed computing elements (e.g., memories, processing cores,switches, ports, and/or other computing or network resources). Afronthaul and/or backhaul network communicatively coupling thegeographically distributed computing elements can function as a computerbus.

The processors are communicatively coupled together via at least onenetwork, such as a backhaul network 115. The backhaul network 115 cancomprise an optical fiber network, a wireline network (e.g., Ethernet orother cable links), a wireless network, or any combination thereof. Insome aspects, the backhaul network 115 can comprise the RAN, theInternet, and/or one or more network fabrics (including terrestrialnetwork fabrics, airborne network fabrics, space network fabrics, andcombinations thereof). In one aspect, each of N processors is programmedto function as one of a plurality N of virtual base stations111.1-111.N. In another aspect, each virtual base station 111.1-111.Ncomprises multiple processing cores. In some aspects, each virtual basestation 111.1-111.N represents a hardware abstraction wherein details ofhow the hardware is implemented are concealed within the representationof each “processor” 111.1-111.N as a single element. In such aspects,the physical implementation of each processor 111.1-111.N can comprisephysical computing elements that are geographically distributed and/orphysical computing elements that are shared by multiple virtual basestations 111.1-111.N.

Each virtual base station 111.1-111.N can be distributed across aplurality of processors and memories. By way of example, a virtual basestation 111.1-111.N can comprise software instructions residing on oneor memories near the RAN edge (e.g., on BTS 101.1-101.N) and configuredto operate one or more RAN-edge processors. The RAN-edge portion of thevirtual base station 111.1-111.N can be configured to performlatency-sensitive RAN processing operations and may include a mobilitysource-code segment configured to migrate the virtual base station111.1-111.N portion from one network device to another, such as when itsassociated UE moves through the network. The virtual base station111.1-111.N can also comprise software instructions residing on one ormemories farther away from the RAN edge (such as near or within the corenetwork) configured to operate one or more processors, such as locatedin the central processor 110, in a BTS configured to function as a hubor central processor, and/or in a remote data center. The core-portionof the virtual base station 111.1-111.N can be configured to perform RANprocessing operations that are less latency-sensitive.

By way of example, each virtual base station 111.1-111.N may compriseone or more of the processors and perform base station processingoperations that would ordinarily be performed solely by one of thecorresponding base stations 101.1-101.N. Specifically, virtual basestations can be implemented via software that programs general-purposeprocessors. For example, an SDR platform virtualizes baseband processingequipment, such as modulators, demodulators, multiplexers,demultiplexers, coders, decoders, etc., by replacing such electronicdevices with one or more virtual devices, wherein computing tasksperform the functions of each electronic device. In computing,virtualization refers to the act of creating a virtual (rather thanactual) version of something, including (but not limited to) a virtualcomputer hardware platform, operating system (OS), storage device, orcomputer network resources.

In accordance with the art of distributed computing, a virtual basestation's functions can be implemented across multiple ones of theplurality of processors. For example, workloads may be distributedacross multiple processor cores. In some aspects, functions for morethan one base station are performed by one of the processors.

As used herein, distributed computing refers to the use of distributedsystems to solve computational problems. In distributed computing, aproblem is divided into multiple tasks, and the tasks are solved bymultiple computers which communicate with each other via messagepassing. A computer program that runs in a distributed system isreferred to as a distributed program. An algorithm that is processed bymultiple constituent components of a distributed system is referred toas a distributed algorithm. In a distributed computing system, there areseveral autonomous computational entities, each of which has its ownlocal memory.

In accordance with aspects of the disclosure, the computational entities(which are typically referred to as computers, processors, cores, CPUs,nodes, etc.) can be geographically distributed and communicate with eachother via message passing. In some aspects, message passing is performedon a fronthaul and/or backhaul network. The distributed computing systemcan consist of different types of computers and network links, and thesystem (e.g., network topology, network latency, number of computers,etc.) may change during the execution of a distributed program. In oneaspect, a distributed computing system is configured to solve acomputational problem. In another aspect, a distributed computing systemis configured to coordinate and schedule the use of shared communicationresources between network devices. In some aspects, the virtual basestations 111.1-111.N are implemented as middleware, each residing on oneor more network devices, and in some cases, each distributed acrossmultiple network devices for accessing either or both RAN-edge servicesand core services. Such implementations can comprise “fluid” middleware,as the virtual base stations 111.1-111.N (or at least the distributedcomponents thereof) can migrate from one network device to another, suchas to reduce latency, balance processing loads, relieve networkcongestion, and/or to effect other performance and/or operationalobjectives.

A distributed computing system can comprise a grid computing system(e.g., a collection of computer resources from multiple locationsconfigured to reach a common goal, which may be referred to as a supervirtual computer). In some aspects, a distributed computing systemcomprises a computer cluster which relies on centralized management thatmakes the nodes available as orchestrated shared servers. In someaspects, a distributed computing system comprises a peer-to-peercomputing system wherein computing and/or networking comprises adistributed application architecture that partitions tasks and/orworkloads between peers. In some aspects, peers are equally privileged,equipotent participants in the application. They are said to form apeer-to-peer network of nodes. Peers make a portion of their resources,such as processing power, disk storage, network bandwidth, etc.,available to other network participants without the need for centralcoordination by servers or stable hosts. Peers can be either or bothsuppliers and consumers of resources. Distributed computing includesCloud computing.

In some aspects, the central processor resides at the edge of the RANnetwork. The central processor 110 can provide for base-stationfunctionality, such as power control, code assignments, andsynchronization. The central processor 110 may perform network loadbalancing (e.g., scheduling RAN resources), including providing forbalancing transmission power, bandwidth, and/or processing requirementsacross the radio network. Centralizing the processing resources (i.e.,pooling those resources) facilitates management of the system, andimplementing the processing by employing multiple processors configuredto work together (such as disclosed in the '163 application) enables ascalable system of multiple independent computing devices, wherein idlecomputing resources can be allocated and used more efficiently. In someaspects, a portion of the central processor resides at the edge(s) ofthe RAN and a portion resides in at least one remote location (such as adata center). RAN processing tasks can be partitioned based on latencysensitivity such that latency-sensitive tasks are assigned to edgecomputing resources and tasks that are not as latency-sensitive areassigned to remote computing resources.

In some aspects, base-station functionality is controlled by individualbase transceiver stations and/or UEs assigned to act as base stations.RAN processing (such as, but not limited to, array processing) may beperformed in a distributed sense wherein channel estimation, weightcalculation, and optionally, other network processing functions (such asload balancing) are computed by a plurality of geographically separatedprocessors. In some aspects, access points and/or subscriber units areconfigured to work together to perform computational processing. Acentral processor (such as central processor 110) may optionally controldata flow and processing assignments throughout the network. In suchaspects, the virtual base stations 111.1-111.N (or components thereof)can reside on UEs, relays, and/or other RAN devices.

Distributed virtual base stations 111.1-111.N can reduce fronthaulrequirements by implementing at least some of the Physical Layerprocessing at the base transceiver stations 101.1-101.N whileimplementing other processing (e.g., higher layer processing, or thehigher layer processing plus some of the Physical layer processing) atthe central processor 110. In some aspects of the disclosure, one ormore of the base transceiver stations 101.1-101.N depicted in thefigures may be replaced by UEs adapted to perform as routers, repeaters,and/or elements of an antenna array.

In one aspect of the disclosure, the base station network comprisingbase transceiver stations 101.1-101.N is adapted to operate as anantenna array for MIMO subspace processing in the RAN. In such aspects,a portion of the network may be adapted to serve each particular UE. TheSDRs (represented as the virtual base stations 111.1-111.N) can beconfigured to perform the RAN baseband processing. Based on the activeUEs in the RAN and the standard(s) they use for their wireless links,the SDRs can instantiate virtual base station processes in software,each process configured to perform the baseband processing that supportsthe standard(s) of its associated UE(s) while utilizing a set of thebase transceiver stations within range of the UE(s).

In accordance with one aspect of the disclosure, baseband waveformscomprising RAN channel measurements and/or estimates (such as collectedby either or both the UEs and the base transceiver stations) areprocessed by the SDRs (such as in a Spatial Multiplexing/Demultiplexingmodule (not shown)) using Cooperative-MIMO subspace processing toproduce pre-coded waveforms. A routing module (not shown) sends thepre-coded waveforms over the fronthaul 105 to multiple ones of the basetransceiver stations 101.1-101.N, and optionally, to specific antennas102.1-102.M₁, 103.1-103.M₂, . . . , 104.1-104.M_(N). The basetransceiver stations 101.1-101.N can be coordinated to concurrentlytransmit the pre-coded waveforms such that the transmitted waveformspropagate through the environment and constructively interfere with eachother at the exact location of each UE 120.1-120.K.

In one aspect, the super-array processing system 111 configurescomplex-weighted transmissions 122, 123, and 124 from the geographicallydistributed base transceiver station 101.1, 101.2, and 101.N,respectively to exploit the rich scattering environment in a manner thatfocuses low-power scattered transmissions to produce a concentratedhigh-power, highly localized signal (e.g., coherence zones 125.1, 125.2,. . . , 125.K) at each UE's 120.1-120.K antenna system 121.1, 121.2, . .. , 121.K, respectively. The coherent combining of the transmittedwaveforms at the location of each UE 120.1-120.K can result in thesynthesis of the baseband waveform that had been output by the SDRinstance associated with that particular UE 120.1-120.K. Thus, all ofthe UEs 120.1-120.K receive their own respective waveforms within theirown synthesized coherence zone concurrently and in the same spectrum.

In accordance with one aspect of the invention, each UE's correspondingsynthesized coherence zone comprises a volume that is approximately acarrier wavelength or less in width and centered at or near each antennaon the UE. This can enable frequency reuse between nearby—evenco-located—UEs. Spatial Multiplexing/Demultiplexing can be configured toperform maximum ratio processing. Any of various algorithms for MIMOprocessing disclosed in the incorporated references may be employed bymethods and apparatus aspects disclosed herein. Some aspects cancomprise zero forcing, such as to produce one or more interferencenulls, such as to reduce interference from transmissions at a UE that isnot an intended recipient of the transmission. By way of example, butwithout limitation, zero forcing may be performed when there are a smallnumber of actual transmitters (e.g., base transceiver station antennas)and/or effective transmitter sources (e.g., scatterers in thepropagation environment).

In alternative aspects, at least one of the BTSs is configured totransmit downlink signals without spatial precoding. In such cases, theUEs receiving such downlink transmissions might be configured to performspatial processing.

By way of example, some aspects of the disclosure configure the UEs120.1-120.K to form a cluster in which the individual UEs 120.1-120.Kare communicatively coupled together via a client device fronthaulnetwork 102, which can comprise any of various types of local areawireless networks, including (but not limited to) wireless personal areanetworks, wireless local area networks, short-range UWB networks,wireless optical networks, and/or other types of wireless networks. Insome aspects, since the bandwidth of the client device fronthaul network102 is typically much greater than that of the WWAN, a UE 120.1-120.Kcan share its access to the RAN (i.e., its WWAN spatial subchannel, orcoherence zone) with other UEs 120.1-120.K in the cluster, thus enablingeach UE 120.1-120.K to enjoy up to a K-fold increase in instantaneousdata bandwidth.

In some aspects, a cluster of UEs can perform cooperative subspacedemultiplexing. In some aspects, the cluster can perform cooperativesubspace multiplexing by coordinating weighted (i.e., pre-coded)transmissions to produce localized coherence zones at other clustersand/or at the base transceiver stations 101.1-101.N. In some aspects,the UEs 120.1-120.K comprise a distributed computing platform configuredto perform distributed processing (and optionally, other cloud-basedservices). Distributed processing may be performed for Cooperative-MIMO,other various SDR functions, and/or any of various network control andmanagement functions.

Thus, each UE may comprise a distributed SDR, herein referred to as adistributed UE SDR. Components of the distributed UE SDR can reside onmultiple network devices, including UEs, relays, BTSs, access points,gateways, routers, and/or other network devices. Components of thedistributed UE SDR can be communicatively coupled together by anycombination of a WPAN (such as may be used for connecting an ecosystemof personal devices to a UE), a peer-to-peer network connecting UEstogether and possibly other devices, a WLAN (which may connect UEs to anaccess point, router, hub, etc.), and at least one WWAN. In someaspects, distributed UE SDR components can reside on a server connectedvia a gateway or access point. In some aspects, distributed UE SDRcomponents can reside on one or more BTSs, WWAN hubs, WWAN relays, andcentral processors, and/or on network devices in the core network.

Transmitter apparatuses are proposed according to some aspects of thedisclosure as schematically shown in FIG. 2A, such as may be used in thedownlink transmission system comprising the BTSs 101.1-101.N as shown inFIG. 1. Such a transmitter apparatus comprises a code divisionmultiplexer 201 having signal inputs for receiving original data symbols(e.g., comprising separate user-data streams) to be transmitted in aplurality of code division multiple-access channels employing the sameset of subcarriers in a shared WWAN radio access (e.g., a RAN downlink)channel. The code division multiple-access channels may be received andde-multiplexed by each of a plurality of UEs. The multiplexer 201 mayalso have a signal input for control information to be transmitted inthe downlink channel. The multiplexer 201 maps each original data symbol(and optionally, may include control information symbols) to aspread-DFT code (e.g., codeword). The codes may comprise orthogonalcodes, quasi-orthogonal codes, or some combination thereof. In aspectsdisclosed herein, the multiplexer 201 can be operable to multiplex eachof a plurality of data streams into a different one of a plurality ofspread-DFT code division multiple-access channels.

In one aspect, the multiplexer 201 can assign a different codeword setto each data stream to be transmitted. A codeword set can comprise oneor more spread-DFT codes, and each set can comprise a different codedivision multiple access channel. For example, each data symbol ismapped to one of the DFT codewords in its stream's assignedmultiple-access codeword set (e.g., channel). This enables each SC-FDMAsymbol generated therefrom to comprise a plurality of code-divisionmultiple-access channels while providing a low-PAPR OFDM transmissionsignal. An SC-FDMA symbol is sometimes described as containing Nsub-symbols that represent the modulating data. In LTE, the OFDMA(downlink) and SC-FDMA (uplink) symbol lengths are both 66.7 μs. Inaspects of the disclosure, SC-FDMA coding is adapted so it can beimplemented in the downlink. In some aspects of the disclosure, adownlink SC-FDMA symbol comprises N spread-DFT symbols, wherein anN-point DFT (which may be implemented using an FFT) is employed forgenerating the spread-DFT symbols.

A DFT spreader 202 spreads the original data symbols (and optionally,each control information symbol) into spread data symbols. A mapper 203maps the spread data symbols to OFDM subcarriers (and optionally, toantennas), such as to input bins of an oversampled inverse discreteFourier transform (IDFT) 204, which is typically implemented as anoversampled fast transform (e.g., an FFT). To provide the low-PAPRcharacteristics of the OFDM transmission signal, the spread-DFT symbolscan be mapped to contiguous or non-contiguous (but evenly spaced)subcarriers. The spread-OFDM signal output from the IDFT 204 isprepended with a cyclic prefix (in “+CP” circuit 205) beforeup-conversion to RF and amplification in an RF transmitter (e.g., RFfront-end) 206.

In spread-OFDM, N subcarriers can be shared by every original datasymbol in a block of up to N original data symbols if the spreadingcodes are configured to be orthogonal. The spreader 202 enables the Nsubcarriers to be shared by a block of up to N original data symbols,which the multiplexer 201 selects from the user data and which cancomprise multiple UE transport blocks.

In one aspect, the function of the spreader 202 can be explained asfollows. Each original data symbol of the block is replicated into Nparallel copies. Each copy is then multiplied by a code chip from acorresponding spreading signature. A spreading signature can comprise arow or column of a DFT-based spreading matrix, and may be referred to asa spreading code, a codeword, or a code space. The products are summedsuch that each sum (referred to as a spread data symbol) comprises oneof N linear combinations of the original data symbols, wherein thecoefficients are the code chips (e.g., a row or column of acorresponding spreading matrix), and the unknowns are the original datasymbols. Each spread data symbol is modulated onto a different one ofthe N subcarriers, all of which are to be transmitted in parallel. EachSC-FDMA symbol comprises N spread data symbols. Thus, the multiplexer201 operates in conjunction with the spreader 202 to map data symbolsfrom a plurality of data streams (intended for different destinationdevices) into each SC-FDMA symbol, thereby providing an OFDMmultiple-access signal that has low PAPR.

The usual implementation of OFDM calls for the IDFT 204 to convert theparallel chips into serial form for transmission. In OFDM, the IDFT 204is typically implemented via oversampling, so the input symbol block tothe IDFT 204 is typically zero-padded, since zero padding in one domain(e.g., time or frequency) results in an increased sampling rate in theother domain (e.g., frequency or time). The cyclic prefix is appended toremove the interference between successive symbols and to accommodatethe circulant convolution provided by the FFT.

In some aspects, the multiplexer 201 can comprise a physical memorystorage, such as a data buffer configured to temporarily store databefore it is input to the DFT spreader 202. The data can be stored inthe buffer as multiple data streams are retrieved from an input device(e.g., one or more data sources, which are not shown) and/or before itis sent to an output device (e.g., the DFT spreader 202). The datastored in a data buffer is stored on a physical storage medium. Bufferscan be implemented in software, and typically use RAM to store temporarydata due to the much faster access time compared with hard disk drives.The multiplexer 201 can employ a cache, which can function as a buffer.The multiplexer 201 can comprise non-transitory computer-readable memorywith instructions stored thereon and configured to operate a processorto order, group, or otherwise arrange the data in the buffer (or cache)to multiplex each of the data streams into a different one of aplurality of spread-DFT code division multiple-access channels. Anintegrated circuit or other circuits might be designed to provide thisfunctionality. The multiplexer 201 may comprise or be communicativelycoupled to a scheduler (not shown) that assigns each data stream to amultiple-access code space. The multiplexer 201 then arranges the datasuch that when it is partitioned into length-N blocks by the DFTspreader 202, data from each stream is mapped to the code set of itsassigned multiple-access channel.

The DFT spreader 202 can implement an FFT algorithm that computes theDFT of an input sequence received from the multiplexer 201. FFTalgorithms are well-known in the art and include the Cooley-Tukeyalgorithm, Prime-factor FFT algorithm, Bruun's FFT algorithm, Rader'sFFT algorithm, Bluestein's FFT algorithm, and Hexagonal Fast FourierTransform. Other FFT algorithms may be employed. A serial-to-parallelconverter may convert a received data sequence into parallel inputs. TheDFT spreader 202 can comprise an input data partitioner to partitioninput data into blocks of N data symbols. The DFT spreader 202 can beimplemented by an integrated circuit, for example. In some aspects, theDFT spreader 202 can comprise non-transitory computer-readable memorywith instructions stored thereon and configured to operate a processorto perform the spreading.

The mapper 203 can comprise a combination of physical memory storage(such as a buffer) and a data transit mechanism (such as aserial-to-parallel converter, a parallel-to-serial converter, aswitching array, etc.) to effect the mapping of symbols output from theDFT spreader 202 to inputs of the IDFT 204. For example, the mapper 203may employ a serial-to-parallel converter to convert a serial datastream into parallel inputs to the IDFT 204, and the mapper 203 mayfurther comprise a zero-insertion algorithm or circuit to insert zerovalues into the serial data stream according to scheduling information(such as resource block assignments for a predetermined set of UEs). Themapper 203 can comprise a data insertion module for receiving controlsymbols (including reference symbols) to be mapped to predeterminedsubcarriers. The mapper 203 can be implemented in an integrated circuit.In some aspects, the mapper 203 can comprise non-transitorycomputer-readable memory with instructions stored thereon and configuredto operate a processor to perform the spreading.

IDFT 204 can be implemented via circuits and processors typicallyemployed in OFDM. The IDFT 204 can be implemented via an FFT and canemploy zero padding. A parallel-to-serial conversion can provide theoutput OFDM transmission signal.

In some aspects, a PAPR-mitigation processor may process the datasymbols prior to input to the multiplexer 201. For example, aspects ofthe disclosure can be configured to employ a first set of spreadingcodes (such as orthogonal and/or quasi-orthogonal spreading codes)designed to spread original data symbols to produce first spread datasymbols. The first spreading codes may be configured to produce firstspread data symbols with lower PAPR than the original data. Themultiplexer 201 might comprise a first spreader (not shown) to performsuch first spreading. Alternatively, the first spreader (not shown)might be implemented before the multiplexer 201 or in place of themultiplexer 201. The first spreader (not shown) can be configured tospread each stream's data symbols separately from the other stream(s).The first spread data symbols are subsequently spread with DFT-basedcodes by DFT spreader 202 to produce second spread data symbols, whichare subsequently mapped to OFDM resource blocks by mapper 203 and thenmodulated onto OFDM subcarriers by IDFT 204. A corresponding receiveraccording to this aspect can demodulate the received signals (e.g., viaa DFT), optionally equalize the demodulated signal (e.g., via afrequency-domain equalizer), de-map the resulting symbols (e.g., via ade-mapper, and possibly a scheduler), perform DFT de-spreading (e.g.,via a de-multiplexer decoder comprising a DFT de-spreader, and possiblya de-multiplexer configured to provide the DFT de-spreader withde-spreading codes corresponding to the receiver's multiple-accesschannel(s)), and perform second de-spreading of the resultingDFT-despread (and possibly de-multiplexed) symbols (e.g., by a secondde-spreader or a baseband data processor comprising a secondde-spreader).

In a receiver configured to receive spread-OFDM signals (such as thereceiver block diagram depicted in FIG. 3A), a received spread-OFDMtransmission is filtered, converted to baseband, and digitized by an RFreceiver, such as RF front-end 301, and then the cyclic prefix isremoved (such as by a cyclic prefix removal circuit 302 or someequivalent) from the digitized baseband signal. The receiver cancomprise up to N matched filters, which can be implemented in thediscrete baseband domain, such as by performing a DFT 303. Specificoutput values from the DFT 303 may be selected by a de-mapper 304corresponding to subcarriers allocated by a scheduler (not shown) to theUE(s), for example. The output of the DFT 303 has the form of thetransmitted signal multiplied by a diagonal channel matrix whosediagonal values are flat-fading coefficients, which allows for simpleequalization 314. The IDFT 204 and DFT 303 operations and the role ofthe cyclic prefix are implicitly absorbed through the diagonal structureof the channel response. Thus, aspects of the disclosure can provide forconfiguring the spreader 202 to provide various benefits, including (butnot limited to) orthogonal coding, enabling use of a fast-transformalgorithm, and shaping the transmitted OFDM signal to have low PAPR.

In accordance with some aspects of the disclosure, a processor-basedtransceiver can include a non-transitory computer-readable memory withinstructions stored thereon and configured to perform any of thealgorithms disclosed herein. In reference to the spreader 202, by way ofexample, each original data symbol in a length-N block can be multipliedby a complex-valued spreading code, such as via a matrix multiplicationor equivalent operation. For example, a j^(th) original data symbold_(j) is multiplied by a j^(th) column vector of an N×N spreading matrixS, where the j^(th) column vector corresponds to the spreading code forsymbol d_(j), and N (which equals the number of subcarriers onto whichthe spread data is modulated) corresponds to the bandwidth expansionfactor (e.g., spreading gain) to produce a j^(th) spread data-symbolvector. The multiplexer 201 (which may be in communication with ascheduler) can select user data for different UEs (and optionally,control information symbols) and arrange the selected data to producethe length-N block of input data symbols to the spreader 202, thusproviding for code division multiplexing (e.g., code division multipleaccess). Thus, the multiplexer 201 can map each user data stream to aspread-DFT code set assigned by the scheduler to the corresponding UE.The N different spread data vectors are summed to produce a vector ofspread data symbols (of length N) before serial-to-parallel conversion,zero insertion (e.g., zero padding), and processing by the IDFT 204. Itshould be appreciated that if fewer than N original data symbols (e.g.,n<N) are in the input block, then N−n of the symbols in the block may beset to zero while still producing a length-N vector of spread datasymbols.

FIG. 2B is a block diagram of a DFT spreader in accordance with someaspects of the disclosure. A code-division multiplexer 230 receivesscheduling information and/or generates scheduling information thatcomprises an assignment of each user-data streams (and optionally,control information data) to a code set (e.g., one or more codewords)generated by the spreader 233. Layer mapper 231 is optionally provided,which is responsive to scheduling information to assign data symbols todifferent layers, which can be mapped to corresponding transmitantennas. This may be performed by one or more BTSs, remote radio heads,relays, access points, etc., for downlink transmissions. In someaspects, this may be performed for uplink transmissions. Layer mapper231 might be configured to map different user data (and optionally,control information data) to different time slots in the downlinktransmissions. Spreading code selector 232 obtains coding parameters,such as subcarrier information (e.g., number of subcarriers N,subcarrier spacing, and/or the like), time-slot information, and/orlayer information, which can be used to select or adapt spreadingperformed by spreader 233.

The spreading code selector 232 can be configured to select spreadingcodes corresponding to criteria, such as code-space orthogonality (e.g.,orthogonal and/or quasi-orthogonal spreading codes), PAPR criteria,and/or enabling a fast transform operation for code generation and/orfor encoding original data symbols. Responsive to the number of assigneduplink subcarriers (for example), the selector 232 can select a set oforthogonal complex spreading codes, whereas the multiplexer 230 canassign each data symbol to one (or more) of the spreading codes.Orthogonal functions (e.g., signals or sequences) have zerocross-correlation. Zero correlation occurs if the product of two signalssummed over a period of time (or sequence length) is zero. A set ofsignals or sequences in which all have zero cross-correlation with eachother constitutes an orthogonal code space(s).

Other criteria may be employed. For example, a criterion which relatesto pulse shaping (e.g., time-domain and/or frequency-domain shaping, orwindowing) can further reduce PAPR by sacrificing some bandwidthefficiency. In one aspect, a mask (e.g., a spectral mask) may be appliedto the subcarriers, such as by way of the coding or directly followingthe coding, in order to shape the spread-OFDM signal, such as to providefor pulse shaping.

In one aspect, spreading is achieved via a fast transform operation(such as FFT spreader 233). The FFT spreader's 233 input parameters canbe controlled by the spreading code selector 232 in accordance with thecriteria and/or coding parameters. In one aspect, FFT spreader 233parameters, such as FFT size, input data block size, input symbol order,etc., can be controlled by the spreading code selector 232. In someaspects, the selector 232 can select how a fast transform is performed,such as by directly controlling the transform's operations or byindirectly controlling the transform via FFT size, and the like.

In one aspect, responsive to an assignment of N OFDM subcarriers, theselector 232 selects an orthogonal N×N complex spreading matrix thatcomprises DFT coefficients. Some matrices comprising DFT coefficientsare not orthogonal. While it is well known that some orthogonalfunctions can be generated or expanded using various algorithms, such asa seed algorithm or some other recursive technique, some of thesealgorithms do not provide codes with desirable features, such asorthogonality and low PAPR. For example, an N×N spreading matrixconstructed by concatenating rows or columns of an N/2×N/2 DFT spreadingmatrix can yield fewer than N orthogonal spreading codes. Similardeficiencies result from concatenations and other combinations ofdifferent-size DFT matrices, permutations of DFT matrices, punctured DFTmatrices, truncated DFT matrices, and the like. Thus, in some aspects,the selector 232 advantageously provisions an N×N spreading matrix (orcorresponding set of complex codes) to provide for N orthogonalspreading codes. This can be referred to as an orthogonal code spacewith dimension N.

In some aspects of the disclosure, the selector 232 can provide fororthogonally spreading a block of up to N original data symbols withDFT-based complex spreading codes to produce a length-N vector of spreaddata symbols. In other aspects, the selector 232 can employ complexspreading codes to spread N′>N original data symbols onto N subcarriers.While these complex spreading codes are not all orthogonal, the codescan be configured to have low cross correlation. Various techniques maybe employed to select a code set having optimal features, such as lowcross correlation, low PAPR, or a combination thereof. In some aspects,at least some of the spreading codes can be orthogonal to each other.

FIG. 3B is a block diagram that depicts a portion of a receiver, such asa receiver that may be employed in a UE. In one aspect, the decoder 305comprises the system shown in FIG. 3B. A code selector 352 can processsubcarrier parameters corresponding to the received spread-OFDM signalto control decoder 353. The code selector 352 can be responsive to thespreading code(s) assigned to the UE by a scheduler and provide for acorresponding code set to enable decoder 353 to decode the UE's spreaddata. The decoder 353 can employ a fast transform, such as an IFFT, tode-spread the spread data symbols and produce de-spread data symbols,which may be output for further processing. A digital baseband inputrepresenting the received downlink signal is provided by processor 355to the decoder 353. In one aspect, processor 355 can provide spread datasymbols comprising spread user data symbols, spread control signals, orboth to the decoder 353. The de-mapped data processor 355 may be part ofthe de-mapper 304, or it may be part of the decoder 305. Since theserver side of the WWAN can schedule the downlink OFDM subcarriers andcodes used by each UE, the spreading code and subcarrier parameters canbe retrieved from a UE scheduler 351 that receives control informationin the downlink. The UE scheduler 351 can be responsive to schedulinginformation transmitted in the RAN downlink to control the demapper 355(e.g., for OFDM subcarrier selection) and the code selector 352 (e.g.,for code-space selection).

In accordance with one aspect of the disclosure, as depicted in FIG. 4A,a method performed in a radio transceiver is provided, which can employSC-FDMA to produce a multiple-access OFDM transmission signal withreduced PAPR. In some aspects, the method depicted in FIG. 4A (as wellas any of the methods throughout this disclosure) comprises functionalsteps implemented via software instructions operable to cause aprocessor (such as a general-purpose processor) to execute the steps ina process which produces a spread-OFDM signal. In some aspects, one ormore of the functional steps are embodied in hardware, such as circuits.

By way of example, application-specific integrated circuits (ASICs),field-programmable gate arrays (FPGAs), and/or other circuits can beprovided as embodying one or more of the functional steps disclosedthroughout the specification and depicted in the drawings. In someaspects, multiple ones of the functional steps can be implemented by acommon processor or circuit. For example, certain efficiencies might beachieved by configuring multiple functional steps to employ a commonalgorithm (such as an FFT and/or some other algorithm), thereby enablinga circuit, a processor, or some other hardware component to be used fordifferent functions, and/or enabling software instructions to be sharedfor the different functions.

With respect to FIG. 4A, an eNodeB receives a Channel quality indicator(CQI) and Buffer Status Reports (BSRs) from each UE 401. Each UE maycompute its CQI value from downlink channel and send it to the eNodeB.CQI is a four digit value sent as a feedback for the downlink channel.The CQI informs the eNodeB about the channel quality in the downlink.This helps the eNodeB to allocate proper Modulation and Coding Scheme(MCS) and PRB (Physical Resource Block) for the UE. A BSR indicates tothe network that a UE has certain data in its buffer and requiresresource grants to send this data.

The eNodeB sends MCS, PRB mapping, and code assignment(s) to each UE402. Based on BSR, CQI, and UE Quality of Service (QoS), the eNodeBcomputes the MCS value and PRB mapping information and sends it to theUE in the downlink. QOS defines how a particular user data should betreated in the network. QoS is implemented between the UE and PDNGateway and is applied to a set of bearers. For example, VoIP packetsare prioritized by the network compared to web browser traffic. Otherfactors, such as traffic volume and radio conditions can affectscheduling. Additionally, code assignments for each of the UEs can becomputed and broadcast.

In some aspects of the disclosure, the eNodeB groups UEs having similarmodulation schemes into the same PRB 403. In some cases, UE data streamshaving different modulation orders are mapped to the same PRB. In suchcases, the eNodeB can group UE data streams in the same PRB according tomodulation order such that a first grouping contains UE data streamshaving a first modulation order (e.g., QPSK), a second grouping containsUE data streams having a second modulation order (e.g., 16-QAM), and athird grouping contains UE data streams having a third modulation order(e.g., 64-QAM).

In some aspects, each UE transmission signal is provided with one of aset of different scaling factors by the eNodeB. Such scaling factors canadapt the transmit power of the downlink signal to each UE. In suchcases, the eNodeB can group UE data streams into the same PRB accordingto modulation order and scaling factor such that each grouping comprisesa plurality of UE data streams with both similar modulation order andscaling factor. A scheduler coupled to the code-division multiplexer canperform such groupings described herein. Each of a plurality ofdifferent PRBs may be assigned to a different layer and/or thecorresponding OFDM signals amplified by a different power amplifier.

A code-division multiplexer in the eNodeB assigns a multiple accessspreading code set to each of a plurality of UE data streams in agrouping to multiplex the streams in the downlink channel 404. Thespreading code set can correspond to one or more spreading codes in asingle SC-FDMA symbol interval or in multiple SC-FDMA symbol intervals.Multiple SC-FDMA symbol intervals can comprise a block of consecutivesymbol intervals and/or non-consecutive symbol intervals, such asinterleaved symbol intervals. In one example, the code-divisionmultiplexer combines data symbols from different UE data streams in agrouping to produce one or more length-N blocks of multiplexed UE datasymbols, where N is the number of OFDM subcarriers in the grouping'sPRB.

The position of each data symbol in the block determines the codeassigned to it. In some aspects, data symbols for each user are groupedtogether in the block. In some aspects, data symbols for different usersare interleaved in the block. The number of a UE's data symbols in eachblock can be selected by the code-division multiplexer based on thedownlink data rate scheduled for serving the UE. In some aspects,additional symbols can be inserted into the block. For example, symbolinsertion of repeated symbols or dummy symbols may be performed by thecode-division multiplexer to ensure a low-PAPR signal is amplified bythe eNodeB. In some aspects, control-information symbols are assigned toone or more blocks. In some aspects, the code-division multiplexerschedules a time slot comprising consecutive SC-FDMA symbol intervalscomprising original UE data symbols having the same modulation order,and possibly the same (or similar) scaling factor. In other aspects, thecode-division multiplexer schedules each block to one of a plurality oflayers according to the block's modulation order (and, optionally,scaling factor). Each layer might be directed to a different antenna orto a different power amplifier, for example.

A DFT-spreader (e.g., a SC-FDMA spreader) spreads each data symbol withits assigned code 405. A length-N block of spread symbols is generatedfor each input length-N block of data symbols, for example. A resourcemapper maps each block of spread symbols to its corresponding PRBsubcarriers 406, such as frequency bins of an IFFT. Then each block ofspread symbols is modulated onto its corresponding OFDM subcarriers 407.Additional processing, such as appending a cyclic-prefix (not shown),may follow.

FIG. 4B is a flow diagram that can be employed in accordance withvarious aspects of the disclosure, such as for processing receivedspread-OFDM signals. In one aspect, for example, the method depicted inFIG. 4B is performed by a UE operating on received downlink signals.

The UE transmits CQI and BSRs to one or more eNodeBs 411 and receivesMCS, PRB mapping, and one or more code assignments 412 in response.Downlink user data transmissions are received and processed to produce adigital baseband signal 413. The baseband OFDM signal is demodulated 414(e.g., by an FFT) based on the PRB assigned to the UE, and the resultingmeasurement on each OFDM subcarrier may be equalized 416 based on CSI.Then the equalized signal is decoded 417 based on the UE's assignedDFT-based code set, the UE's code set comprising a subset of the DFTcodes (e.g., the full DFT code set) employed by the eNodeB(s) to encodethe PRB.

FIG. 5 is a flow diagram that illustrates a method for processing adownlink shared channel (DL-SCH) in accordance with aspects of thedisclosure. Upper-layer data in the form of transport blocks is theinput to the physical layer. At first, transport blocks 1001.1-1001.Kfor UEs 1-K are each passed through a CRC encoder 1002.1-1002.K, whichappends a CRC to the data. A CRC is used for error detection intransport blocks.

Each data block is then turbo coded 1003.1-1003.K. Turbo coding is aform of concatenated coding, consisting of two convolutional encoderswith certain interleaving between them. Rate matching 1003.1-1003.K actsas rate coordinator between preceding and succeeding blocks. The ratematching block creates an output bit stream with a desired code rate.Scrambling (not shown) may follow channel coding/rate matching toproduce a block of scrambled bits from the input bits according to ascrambling sequence. Modulation mapping 1004.1-1004.K maps input bitvalues to complex-valued modulation symbols according to a modulationscheme. Exemplary modulation schemes include, but are not limited to,QPSK, 16QAM, and 64QAM.

Although not shown, layer mapping splits the data sequence into a numberof layers. The terms “layer” and “stream” are sometimes usedinterchangeably. For MIMO, at least two layers are used. The number oflayers is typically less than or equal to the number of antennas.Depending on the channel information available at the eNodeB, themodulation and the precoding of the layers may be different to equalizethe performance. Except for transmission on a single antenna port (inthis case, the symbols are directly mapped onto one layer), there can betwo types of layer mapping: one for spatial multiplexing and the otherfor transmit diversity. In spatial multiplexing, the number of layersmay be adapted to the transmission rank, such as by means of a RankIndicator (RI) to the layer mapping. The RI may be fed back from theUE(s). In the case of transmit diversity, the number of layers isusually equal to the number of antenna ports. The number of layers inthis case is not related to the transmission rank, as transmit-diversityschemes are typically single-rank transmission schemes.

Optionally, precoding is used for transmission in multi-antenna wirelesscommunications. In conventional single-stream beam forming, the samesignal can be emitted from each of the transmit antennas withappropriate weighting (phase and gain) such that the signal power ismaximized at the receiver output. Precoding may be performed fordiversity, beam steering, or spatial multiplexing. The MIMO channelconditions may favor one layer (data stream) over another. if the basestation (eNodeB) is given information about the channel—for example,information sent back from the UE—it can add complex cross-coupling tocounteract the imbalance in the channel. Eigen beam forming may beperformed to modify the transmit signals in order to provide an improvedCINR at the output of the channel.

In FIG. 5, K complex-valued modulated-symbol streams corresponding to KUEs are output by the modulation mapping 1004.1-1004.K. A code-divisionmultiplexer 1005 multiplexes the symbol streams together into blocks oflength N and assigns a DFT spreading code to each symbol in each block.Each block is then processed by a spreader, such as a spread-DFTprocessor 1006, which is also referred to as a transform precoder.

In some aspects of the disclosure, a code division multiple-accessdownlink transmission employing OFDM comprises multiplication between aspreading matrix A and a data vector x in which the number of columns inA equals the number of rows in x. In one example, A is an m×n spreadingmatrix, and the product of A with the n×1 column vector x is Ax=b, wherethe spread data b is an m×1 column vector.

${Ax} = {{\begin{bmatrix}a_{11} & a_{12} & \ldots & a_{1n} \\a_{21} & a_{22} & \ldots & a_{2n} \\\vdots & \vdots & \vdots & \vdots \\a_{m\; 1} & a_{m\; 2} & \ldots & a_{mn}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{n}\end{bmatrix}} = \begin{bmatrix}{{a_{11}x_{1}} + {a_{12}x_{2}} + \ldots + {a_{1n}x_{n}}} \\{{a_{21}x_{1}} + {a_{22}x_{2}} + \ldots + {a_{2n}x_{n}}} \\\vdots \\{{a_{m\; 1}x_{1}} + {a_{m\; 2}x_{2}} + \ldots + {a_{mn}x_{n}}}\end{bmatrix}}$

In some aspects, the number of rows in A is configured to provide thenumber of rows m in the vector b. In some aspects of the disclosure, thespreading matrix A is configured to impart or adapt various propertiesof the spread data b, such as to provide the downlink transmissions witha low PAPR, adapt to the number of used subcarriers, and/or adapt to thenumber of layers.

In one aspect of the disclosure, data vector x is configured to comprisedownlink user data corresponding to different UEs. The data vector x canfurther comprise information corresponding to downlink control. In someaspects, user data and/or control information are selected in order togroup symbols in the data vector x with the same modulation order. Insome aspects, both modulation order and scaling factors are used as abasis for grouping. This can be performed for various reasons, includingproviding the downlink transmissions with a low PAPR.

In some aspects, one or more of the columns of spreading matrix A areselected to provide a set of spreading codes for each user. A separatecode set can be employed for control information. Orthogonal codes canprovide for a code division multiple access scheme to allow multipleusers to share the same subcarriers.

In one implementation, a first orthogonal spreading matrix A₁ isprovided for spreading a first downlink user data vector (e.g., data x₁)corresponding to a first user to generate a first spread (i.e., coded)symbol vector.

${A_{1}x} = {{\begin{bmatrix}a_{11} & 0 & \ldots & 0 \\a_{21} & 0 & \ldots & 0 \\\vdots & \vdots & \vdots & \vdots \\a_{m\; 1} & 0 & \ldots & 0\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{n}\end{bmatrix}} = \begin{bmatrix}{a_{11}x_{1}} \\{a_{21}x_{1}} \\\vdots \\{a_{m\; 1}x_{1}}\end{bmatrix}}$

A second orthogonal spreading matrix A₂ is provided for spreading asecond downlink user data vector (e.g., data x₂, x₃) corresponding to asecond user to generate a second spread (i.e., coded) symbol vector.

${A_{2}x} = {{\begin{bmatrix}0 & a_{12} & a_{13} & 0 \\0 & a_{22} & a_{23} & 0 \\\vdots & \vdots & \vdots & \vdots \\0 & a_{m\; 2} & a_{m\; 3} & 0\end{bmatrix}\begin{bmatrix}\vdots \\x_{2} \\x_{3} \\\vdots\end{bmatrix}} = \begin{bmatrix}{{a_{12}x_{2}} + {a_{13}x_{3}}} \\{{a_{22}x_{2}} + {a_{23}x_{3}}} \\\vdots \\{{a_{m\; 2}x_{2}} + {a_{m\; 3}x_{3}}}\end{bmatrix}}$

Similarly, a K^(th) orthogonal spreading matrix A_(K) is provided forspreading a K^(th) downlink user data vector (e.g., data x_(K))corresponding to a K^(th) user to generate a K^(th) spread (i.e., coded)symbol vector (A_(K)x).

In some aspects of the disclosure, downlink user data for each of aplurality of user devices can be separately encoded (i.e., spread) andthen combined to generate the coded symbols Ax=b. This may be performedat the network edge, or by remote computing resources, such as a datacenter. Each user device, upon receiving downlink transmissions andgenerating a digital baseband signal therefrom (possibly afterperforming equalization and/or multi-user detection), can decode theresulting spread symbol vector by using a corresponding de-spreadingmatrix or equivalent processing methods. For example, the de-spreadingmatrix can comprise a de-spreading code set corresponding to the codeset used to spread the user device's downlink data prior totransmission. In some aspects, the de-spreading code set may compriseone or more rows or columns of the de-spreading matrix. In some aspects,the user device is configured to de-spread a control channel byemploying a de-spreading code set corresponding to the code set used tospread the control information. A de-spreading code may be a complexconjugate of the corresponding spreading code.

In some aspects of the disclosure, the matrix A is a square matrix(i.e., m=n). In some aspects, matrix A is implemented as a DFT matrix.Matrix A may be implemented with complex-valued scaling factors,including amplitude scaling and/or phase offsets. In some aspects,matrix A is derived from values of a DFT matrix.

In code division multiple access communication aspects disclosed herein,a row or column of a DFT matrix is referred to as Spread-DFT code, andcan be used to define an individual communication channel. It is usualin the CDMA literature to refer to codewords as “codes.” In thedownlink, each user device, for example, can be allocated a differentcodeword set, or code set, that encodes its signal, A set can compriseone or more codes. The user device employs a corresponding code set todecode the encoded signal. In some aspects, the corresponding code setcan include complex-conjugates of the codes in the code set used toencode the user's signal. Similarly, a code set can be used to encodedownlink control signals, and user devices can each employ acorresponding code set to decode the downlink control signals.

The spread-DFT matrix has the property that the dot product of any twodistinct rows (or columns) is zero. Each row of a DFT matrix cancorrespond to a Spread-DFT function. Aspects of the disclosure canemploy spreading based on an orthogonal matrix, wherein the matrixcolumn vectors form an orthonormal set. Aspects of the disclosure canemploy an appropriately scaled Fourier-based matrix wherein if it ismultiplied by its conjugate transpose, it yields an Identity matrix. Insome aspects, a scaled DFT matrix is employed wherein the columns haveunit magnitude and are orthogonal to each other. In aspects of thedisclosure, each user device generates (or is otherwise provided with) acorresponding code set for decoding, wherein the code set is derivedfrom the conjugate transpose of the DFT matrix used to spread thedownlink data. The corresponding code set can be scaled in order to haveunit norm.

The spreading and de-spreading matrices can have orthonormal columns.A∈C^(m×n) has orthonormal columns if its Gram matrix is the identitymatrix. The columns have unit norm: ∥a_(i)∥²=a_(i) ^(H)a_(i)=1, and thecolumns are mutually orthogonal: a_(i) ^(H)a_(j)=0, i≠j, wherein “^(H)”denotes Hermitian. The conjugate transpose is also known as the adjointmatrix, adjugate matrix, Hermitian adjoint, or Hermitian transpose.

In some aspects, a product of orthogonal matrices may be employed forspreading. For example, a spreading matrix can be constructed from aproduct of two or more orthogonal matrices of equal size. In someaspects, an orthogonal matrix is employed for coding a data block, anddecoding is effected by matrix multiplication of the coded data blockwith an inverse of the orthogonal matrix or a conjugate transpose of theorthogonal matrix. Sub-matrices of such orthogonal matrices can be usedto multiplex different data streams together, and the orthogonalmatrices can be provisioned to provide a resulting OFDM transmissionsignal with reduced PAPR. Alternatively, one or more quasi-orthogonalspreading matrices may be employed in aspects disclosed herein, whereinsome trade-off is made between orthogonality and PAPR. For example, thespreading-code selector 232 may select a spreading matrix that optimizesa metric comprising some weighted combination of PAPR, bandwidthefficiency, and/or bit-error rate, possibly in response to CQI of UEchannels.

Following the spreading operation 1006, a subcarrier mapper 1007 may beused to map spread symbols to specific OFDM subcarrier frequencies. Forexample, mapper 1007 may couple each spread data symbol to its assignedfrequency bin of an M-point FFT 1008. The FFT 1008 output comprises asuperposition of modulated OFDM subcarriers, which the spreading 1006provides with a reduced PAPR. A cyclic prefix may be appended 1009 tothe FFT output signal, followed by pulse shaping 1010 and quadraturemodulation 1011.

FIG. 6 is a flow diagram depicting a method in accordance to someaspects of the disclosure, which can be implemented, for example, byinstructions stored on one or more non-transitory computer-readablememories and configured to instruct one or more general-purposeprocessors (such as a processor core, a server, a distributed computingsystem, etc.) to perform functions disclosed herein. This flow diagramcan represent functional elements embodied as hardware componentsconfigured to perform the operations disclosed herein.

RF-to-baseband processing 1051 is performed on received radio signals,such as WWAN downlink transmissions received by one or more networkdevices. Processing 1051 can be performed with radio hardwarecomponents, such as one or more antennas, amplifiers, filters, frequencydown-converters, A/D converters, and the like. Cyclic prefix removal1052 can be performed on the digital baseband signal. OFDM demodulationcan be performed using an FFT algorithm 1053 implemented by ageneral-purpose processor or some application-specific integratedcircuit.

Subcarrier de-mapper 1054 can select specific output bins of the FFT1053 corresponding to OFDM subcarriers in the PRB(s) assigned to the oneor more network devices. For example, N subcarrier values in eachSC-FDMA symbol interval are collected and then equalized 1055 prior tobeing grouped into length-N blocks for code division de-multiplexing1056. In some aspects, equalization 1055 can comprise multi-userdetection (MUD) and/or inter-symbol interference cancellation. In oneaspect, MUD comprises spatial de-multiplexing. Spatial de-multiplexingcan comprise processing signal values from each of a plurality ofantenna elements on the device. In some aspects, the device receivessignal values from at least one other device's antennas and may beconfigured to perform joint processing (such as cooperative-MIMO) toseparate a plurality of user channels transmitted on the samesubcarriers.

A block of N equalized symbols in each OFDM symbol interval for thenetwork device is processed by a code-division de-multiplexer 1056. Thenetwork device might process equalized data for other network devices,in which case, it can be configured to perform code-divisionde-multiplexing 1056 for each of a plurality of length-N blocks ofequalized symbols. In such aspects, the code-division de-multiplexer1056 might be parallelized.

The code-division de-multiplexer 1056 employs a code set correspondingto the code set employed by the downlink transmitter to encode the dataaddressed to the network device. For example, the code-divisionde-multiplexer 1056 might receive an assigned downlink code setbroadcast by the scheduler in a WWAN. The downlink code set informationis used by the network device to decode its data from the other userdata transmitted in the physical downlink shared channel. Thecode-division de-multiplexer 1056 might also employ an additional codeset to demultiplex certain control information that is transmitted inthe downlink. In joint-processing scenarios, such as cooperative-MIMO,the network device might employ code sets for other network devices.Once the code-division de-multiplexer 1056 determines the codes it willemploy for decoding the equalized spread symbols, it may generate adecode matrix or select corresponding columns in a predetermined decodematrix. It then performs a matrix multiplication between the decodematrix and the block(s) of equalized symbols to produce estimates of theoriginal data symbols. Data demodulation 1057 and error correction 1058may follow de-multiplexing 1056.

In one aspect of the disclosure, FIG. 7 depicts a set of modules, eachcomprising instructions stored on a non-transitory computer-readablememory and configured to instruct at least one general-purpose processor(such as a processor core, a server, a distributed computing system,etc.) to perform functions disclosed herein. In other aspects, one ormore modules can comprise at least one specific-purpose processor, suchas an application-specific integrated circuit or some other circuit.

A baseband modulator, which can be implemented as a software module701.1, transforms a binary input to a multi-level sequence of complexvalues in at least one of several possible modulation formats, includingbinary phase shift keying (BPSK), quaternary PSK (QPSK), 16-levelquadrature amplitude modulation (16-QAM) and 64-QAM. The modulator 701.1can adapt the modulation format, and thereby the transmission bit rate,to match current channel conditions of the transceiver. The outputsignal is referred to as original data symbols.

In aspects of the disclosure, the baseband modulator can comprise aplurality K of software modules 701.1-701.K or software instantiationscorresponding to K user devices, which can include K UEs being served ina RAN downlink. The modulators 701.1-701.K can be implemented on asingle processor (such as in an eNodeB) or on multiple processors,possibly comprising distributed devices communicatively coupled by anetwork.

In some aspects, the systems disclosed herein can be implemented by acluster of UEs and/or other RAN devices. In one aspect, the modulators701.1-701.K are implemented by processors on different network devices,such as devices that might jointly process signals for uplink RANtransmissions.

User data streams for user 1 to user K are coupled to a spread-DFTcode-division multiplexer 702, which combines the user data streams(possibly with control information) into length-N symbol blocks to bespread by an N-point DFT spreader 703. The multiplexer 702 can employany of various types of grouping schemes to multiplex different userdata streams (and optionally, control information) into the symbolblocks. Symbols corresponding to each user might be groupedconsecutively and/or interleaved with other user data and/or controlinformation. The number of user data symbols in a block can be selectedaccording to a target data rate or QoS.

In some aspects, the DFT spreader 703 employs a DFT spreading matrix,which multiplies each length-N symbol block produced by the multiplexer702. Since each column in the spreading matrix corresponds to adifferent orthogonal spreading code, the position of each symbol in theinput symbol block can constitute a spreading code assignment. Thesespreading code assignments can be broadcast to the UEs to inform them asto which codes to employ for decoding their data from the physicaldownlink shared channel.

The DFT spreader 703 outputs a length-N block of spread symbols, whereineach spread symbol comprises a linear combination of symbols in thecorresponding block that is input to the DFT spreader 703. A resourcemapper, such as downlink resource mapper 704, maps the spread symbols toresource blocks, which constitute a plurality (e.g., N) of OFDMsubcarrier frequencies and at least one OFDM symbol interval. In someaspects, the resource mapper 704 is configured to map each length-Nspread-symbol block to N subcarrier frequencies in a single OFDM symbolinterval. Thus, each of the N spread symbols in a block may be mapped toa single resource element, and each resource element can comprise adifferent one of the N subcarrier frequencies in a single OFDM symbolinterval. In some aspects, the resource mapper 704 receives a referencesignal, which can comprise one or more reference symbols to be modulatedon one or more subcarrier frequencies, possibly at different symbolintervals. The resource mapper 704 can map the reference symbols topredetermined resource elements. The resource mapper 704 may becoordinated with the DFT spreader 703, such as to map a plurality ofspread-symbol blocks to consecutive resource blocks, wherein theplurality of spread-symbol blocks are generated from original datasymbol blocks having similar PAPR, such as original data-symbol blockshaving the same modulation order and/or scaling factor.

The resource mapper 704 might output a zero-padded length-M symbolblock, which is input to an M-point inverse DFT 705. In some aspects,alternative approaches to generating an OFDM signal are employed, andthe resource mapper 704 is appropriately configured to direct an OFDMmodulator to modulate subcarrier frequencies corresponding to assignedresource blocks.

The output of the inverse DFT 705 is an OFDM transmission signalcomprising a superposition of modulated subcarriers. The combination ofthe multiplexer 702 and the spreader 703 is configured to provide thesuperposition, which is a multiple-access signal comprising a pluralityof multiplexed user data streams, with low (i.e., reduced) PAPR.Additional processing, such as appending a cyclic prefix 706, can beperformed.

In one aspect of the disclosure, FIG. 8 depicts a set of modules, eachcomprising instructions stored on a non-transitory computer-readablememory and configured to instruct at least one general-purpose processor(such as a processor core, a server, a distributed computing system,etc.) to perform functions disclosed herein. In other aspects, one ormore modules can comprise at least one specific-purpose processor, suchas an application-specific integrated circuit or some other circuit.

By way of example, but without limitation, the set of modules depictedin FIG. 8 can reside in a UE and be configured to process downlinksignals in a RAN, or the modules can reside within a cluster of devicesconfigured to jointly process received downlink signals in a RAN. Atleast one digital front-end processor 801 converts received downlink RFsignals to a digital baseband symbol stream. A cyclic prefix may beremoved 802, and length-M symbol blocks from the symbol stream are inputto an OFDM demodulator, such as a DFT 803. Values modulated on a UE'sassigned OFDM subcarrier frequencies are selected from the DFT 803output by a subcarrier de-mapper 804. Signals output from the DFT 803 orthe de-mapper 804 may be equalized (not shown) prior to de-spreading.The de-mapped symbols comprise spread user data symbols (and possiblyspread control information), and optionally, reference symbols. Areference-signal processor 814 calculates channel state information,CQI, and/or any other performance indicator from the reference symbols.This information may be transmitted back to eNodeBs in the RAN.

The spread user data symbols intended for the UE (and possibly spreadcontrol information) are decoded in a spread-DFT code divisionde-multiplexer 805. Control information is optionally processed by acontrol-signal processor 815. As described above, the de-multiplexer 805can employ de-spreading codes corresponding to the spread-DFT CDMAchannel(s) assigned to the UE by the radio access network. Thede-multiplexer 805 de-multiplexes (and thus, de-spreads) the UE's userdata from other spread-DFT multiple-access channels in the downlink. Insome aspects, such as when a UE performs joint processing, thede-multiplexer 805 can employ de-spreading codes corresponding to one ormore spread-DFT CDMA channels assigned to at least one other UE. Thede-multiplexer 805 can determine the de-spreading code(s) from controlinformation in a broadcast channel, such as physical downlink controlchannel, for example.

One or more spread-DFT CDMA channels may be assigned for controlinformation. Thus, the de-multiplexer 805 may de-spread controlinformation from the downlink signal, and the control information canoptionally be processed by a control-signal processor 815. De-spreaduser data is typically subject to additional processing operations 806.In some aspects, multi-user detection (including spatialde-multiplexing) may be performed in blocks 805 and/or 806.

As depicted in FIG. 9, a radio transmitter configured in accordance withaspects disclosed herein can include a controller, such as at least onecomputer or data processor, at least one non-transitorycomputer-readable memory medium embodied as a memory that stores aprogram of computer instructions, and at least one suitable radiofrequency (RF) transmitter for wireless communications with at least oneother transceiver via one or more antennas. The exemplary aspects of thedisclosure (including those depicted in the flow diagrams and blockdiagrams) may be implemented, at least in part, by computer softwareexecutable by the data processor. The transmitter shown in FIG. 9 cancomprise an eNodeB or some other type of base transceiver station, arelay, a user device (e.g., a UE), or some other transceiver.

A plurality of user data streams (user data streams 1-K) are input to aPAPR-reduction module 901, which can include a block scheduler 912and/or a block spreader 911. A reduced-PAPR symbol block is output frommodule 901 and coupled into a code division multiplexer 902, whichmultiplexes different user data streams together into symbol blocks thatare spread by a spread-DFT module 903. A PRB mapper, such as asubcarrier mapper 904, maps the spread symbols from the spread-DFTmodule 903 to a PRB that is common to a plurality of user devices. Theplurality of user devices share the same PRB by the implementation ofthe multiplexing 902 and spreading 903, which enables the spreading 903to the OFDM modulator's (e.g., IFFT 905) output signal to have a low(e.g., reduced) PAPR. Additional signal processing modules (e.g., CP &pulse shaping 906, and power amplifier 907) can be provided.

In some aspects of the disclosure, the PAPR of the symbol block outputfrom module 901 affects the PAPR of the superposition signal output fromthe IFFT 905. As the PAPR of the module's 901 output is reduced, asubsequent reduction in the IFFT's 905 output occurs. Thus, the blockscheduler 912 and/or the block spreader 911 can be configured to reducethe PAPR of the superposition signal by reducing the PAPR of the symbolblock output from module 901.

In some aspects, the block scheduler 912 groups user data streams havingsimilar PAPR, such as user data streams having the same modulation orderand that are scheduled to be provided with the same (or similar) scalingfactor. User data streams that are grouped together in this manner arescheduled for the same PRBs. The multiplexer 902 assigns a codeword setto each user data stream, and the user is informed of its assignedcodeword set so it can decode its downlink data stream.

In some aspects, the spreader 903 spreads each input symbol according toits location in the input length-N symbol block. For example, thespreader 903 might perform a matrix multiplication between a DFT matrixand the length-N symbol block vector, or it may perform an FFT operationon the symbol block. In such aspects, the multiplexer 902 effectivelyperforms code assignments by inserting data symbols into specificpositions in the length-N symbol block. In some aspects, the blockscheduler 912 and the multiplexer 902 are configured to generateconsecutive PRBs having similar PAPR.

In some aspects, the block spreader 911 is configured to spread the userdata streams (user data streams 1-K) with one or more spreading codesthat result in reduced PAPR. In some aspects, the spreading code(s) arepredetermined and known by the user devices such that the user devicescan perform de-spreading. In some aspects, information about spreadingcodes employed by the block spreader 911 is communicated to the userdevices, such as in a broadcast channel.

In some aspects, the module 901 comprises both the block spreader 911and the block scheduler 912. The spreader 911 and scheduler 912 may beconfigured to operate in a manner whereby the scheduler selects certainones of the user data streams to be combined and spread by the spreader911 in order to produce a spread signal with reduced PAPR.

FIG. 10 is a block diagram that comprises many of the same components asshown in FIG. 9. An additional time-division multiplexing (TDM)scheduler 1014 is shown coupled to subcarrier mapper 1004. In someaspects, the TDM scheduler 1014 controls subcarrier mapper 1004, such asto consecutively order spread-symbol blocks that correspond to length-Ndata symbol blocks (which are input to spreader 1003) having similarscale and/or modulation order. In some aspects, power amplifier's 1007back-off can be adapted to the PAPR of the superposition signal itamplifies. Since the TDM scheduler 1014 can be configured to reduce therate at which the superposition signal's dynamic range changes, this cansimplify the adaptive back-off control of the power amplifier 1007. Forexample, the TDM scheduler 1014 can reduce the dynamic range's rate ofchange from a symbol-interval time scale, to a time scale comprisingmultiple symbol intervals.

As illustrated in FIG. 10, user data streams 1 and 2 have similarmodulation order and scale, user data streams 3 and 4 have similarmodulation order and scale, and user data streams 5-K have similarmodulation order and scale. The block scheduler 1012 groups user datastreams together that have similar modulation order and scale. Forexample, the output of module 1001 is a signal comprising user datastreams 1 and 2. Code-division multiplexer 1002 can perform anycombination of grouping and interleaving user data streams 1 and 2 intolength-N data symbol blocks, which are spread 1003, mapped 1004, andOFDM-modulated 1005 to produce a superposition signal having reducedPAPR.

The combination of DFT-spreading 1003, mapping 1004, and OFDM-modulating1005 effectively maps each symbol in the length-N data symbol block to acorresponding superposition pulse position in the OFDM modulator's 1005output. Each pulse position corresponds to a spreading-code vector(e.g., a column in a DFT spreading matrix).

In some aspects, the pulses are sinc-shaped, since the Fourier transformof a rectangle function is a sinc function. Since sinc functions have ahigher PAPR than other pulse shapes, it can be advantageous in someaspects to provide frequency-domain windowing at some point before theIFFT 1005. For example, the subcarrier mapper 1004 and/or the spreader1003 can be configured to provide shaping to spread-symbol blocks suchthat when the spread-symbol blocks are provided to the input bins of theIFFT, the edges of the block are tapered or rounded.

This frequency-domain windowing spreads each pulse in the time domain.Thus, the cost of reducing PAPR can be some combination of reducedbandwidth efficiency and increased inter-symbol interference. Forexample, aspects of the disclosure might provide for some combination ofincreasing the inter-pulse spacing in the IFFT 1005 output and acceptingsome interference between adjacent pulses. Alternatively, windowingmight comprise employing subcarriers outside the set of the Nsubcarriers to which the spread symbols are otherwise mapped 1004.

In FIG. 11, PAPR-reduction module 1101 comprises a layer multiplexer1113. Block scheduler 1111. In some aspects, the block scheduler 1111groups user data streams 1 and 2 together, since they have similarmodulation order and scale, and user data streams 5-K are groupedtogether because they have similar modulation order and scale. Forexample, the block scheduler 1111 can produce a plurality L of groupingsbased on modulation and/or scale. The layer multiplexer 1113 can combinethe user data in each grouping into a different layer. In some cases,the layer multiplexer 1113 might combine groupings into a single layer.

As shown in FIG. 11, there can be up to L layers, and the layers areprocessed in parallel by separate processing chains. For example, layer1 is processed by code-division multiplexer 1102.1, spreader 1103.1,mapper 1104.1, IFFT 1105.1, cyclic prefix appender and pulse shaping1106.1, power amplifier 1107.1, and antenna system 1108.1. Layer L isprocessed by code-division multiplexer 1102.L, spreader 1103.L, mapper1104.L, IFFT 1105.L, cyclic prefix appender and pulse shaping 1106.L,power amplifier 1107.L, and antenna system 1108.L.

As shown in FIG. 12, the L separate processing chains might be combinedin a combiner 1208 and share a common antenna system 1209.

FIG. 13 is a block diagram that illustrates components of a radiotransmitter according to some aspects of the disclosure. The functionalblocks depicted herein can comprise steps of a method. In some aspects,one or more of the blocks can be implemented by a processor programmedwith instructions, such as software code residing on a non-transitorycomputer-readable memory.

A modulation mapper 1301.1-1301.K receives as input a plurality K ofuser data bit streams and generates complex-valued symbols from each bitstream to produce K user data streams, which are input to a spatialprecoder 1302.1-1302.N. The spatial precoder 1302.1-1302.N can beconfigured to perform code-division multiplexing of the K user datastreams, followed by spreading by the corresponding code-divisionmultiple-access code space, and then spatial precoding for each of aplurality N of OFDM subcarrier frequencies. A plurality N_(T) ofantenna-array weights (such as corresponding to N_(T) antennas of adistributed antenna system, for example) are generated for each of the Nsubcarrier frequencies. The antenna-array weights for each subcarrierfrequency are mapped by antenna mapper 1303.1-1303.N to N_(T) antennas.A resource mapper 1304.1-1304.N_(T) may be associated with each antennaand configured to assign PRBs to each user data stream. An OFDM signalgenerator 1305.1-1305.N_(T) modulates precoded user data symbols ontotheir corresponding subcarrier frequencies.

With reference to the spatial precoder 1302.1-1302.N, any of varioustechniques are employed for calculating antenna array weights fortransmission of user data in a distributed antenna system. Suchimplementations can be used for downlink transmissions. Any of thesetechniques can be configured to produce additional spatial subchannelsthat can be used to transmit signals that reduce the PAPR oftransmissions amplified by individual power amplifiers in thedistributed antenna system. In such aspects, the distributed antennasystem can be configured to employ additional spatial degrees of freedomto convey signals that can reduce the PAPR at each transmitter orantenna. These PAPR-reduction signals would generally not be detectableby UEs in the downlink, since they occupy spatial subchannels that arenot employed to communicate with any UE. Their primary purpose is toreduce the PAPR of one or more of the individual downlink transmissions,and this objective can be achieved without sacrificing bandwidthefficiency. For example, each subchannel selected for such signaling mayhave been deemed to be too poor for use as a multiple-access channel, oreach such selected subchannel serves a dummy transceiver, which isprovided only for establishing one or more subchannels for PAPRreduction.

It should be appreciated that any of various spatial multiplexing signalprocessing techniques may be employed for precoding the transmissions,including, but not limited to maximum ratio, minimum mean squared error,dirty-paper coding, and zero-forcing techniques.

In some aspects, eigenvalue-decomposition approaches, such as singularvalue decomposition, may be employed for transmitter spatial processing.For example, a MIMO channel formed by the N_(T) transmit antennascomprising multiple transmission nodes (e.g., base stations) and N_(R)receive antennas comprising multiple UEs can be characterized by anN_(R)×N_(T) channel response matrix H for each OFDM subband, whereineach matrix element h_(i,j) of H denotes coupling or complex channelgain between transmit antenna j and receive antenna i. The rank of H isthe sum of non-zero singular values λ_(i) in which each λ_(i)corresponds to an eigenmode of the channel (i.e., an eigen-channel, orsubspace channel). Each non-zero eigenmode can support a data stream,thus the MIMO channel can support k spatial sub-space channels, where kis the number of non-zero eigenvalues λ_(i). In some aspects, the MIMOchannel is assumed to be full rank with S=N_(T)≤N_(R). In some aspects,the MIMO channel is configured to be less than full rank, withD=N_(R)<N_(T).

For data transmission with eigensteering, eigenvalue decomposition canbe performed on a correlation matrix of H to obtain S eigenmodes of H,as follows:

R=H ^(H) ·H=E·Λ·E ^(H),

where R is a correlation matrix of H; E is a unitary matrix whosecolumns are eigenvectors of R; Λ is a diagonal matrix of eigenvalues ofR; and “^(H)” denotes a conjugate transpose.

A unitary matrix U is characterized by the property U^(H)U=I, where I isthe identity matrix. The columns of a unitary matrix are orthogonal toone another, and each column has unit power. The matrix E is also calledan “eigenmode” matrix or a “transmit” matrix and may be used for spatialprocessing by the distributed antenna system to transmit user data onthe S eigenmodes of H. The eigenmodes may be viewed as orthogonalspatial channels obtained through decomposition. The diagonal entries ofΛ are eigenvalues of R, and represent the power gains for the Seigenmodes. The eigenvalues in Λ may be ordered from largest tosmallest, and the columns of E may be ordered correspondingly. Singularvalue decomposition may also be performed to obtain matrices of left andright eigenvectors, which can be used for eigensteering.

For data transmission with eigensteering, the transmitting entity canperform spatial processing for each subband as follows:

z=E·s,

where s is a vector with up to S data symbols to be sent on a particularfrequency subband; and z is a vector with N_(T) spatially processedsymbols for the subband. In general, D data symbols may be sentsimultaneously on D (best) eigenmodes of H for each subband, where1≤D≤S. The D data symbols in s are spatially processed with D columns ofE corresponding to the D selected eigenmodes. In accordance with aspectsof the disclosure, any of the remaining S−D eigenmodes can be employedto reduce the PAPR of at least one of the D transmissions. For example,PAPR-reduction signals can correspond to any of the remaining S−Dcolumns of E.

In some aspects, specific one(s) of the transmitters (for example,transmitters having power constraints, such as due to being batterypowered or otherwise having limited access to power) can be selected forPAPR reduction, and then signals to be transmitted on one or more of theremaining S−D eigenmodes are calculated to provide an acceptable PAPRfor the selected transmitter(s). The PAPR-reduction signals can be afunction of the pre-coding, user data symbols, and/or any power scalingof the subspace channels. In some aspects, the number of transmittingantennas N_(T)=S, and the number of receiving antennas N_(R)=D, so thereis unutilized rank in H that can be exploited for providing PAPRreduction without degrading performance in any of the D eigenmodes. Insome aspects, any of various iterative techniques can be employed tocalculate the PAPR-reduction signals. A trellis exploration algorithmcan be adapted to solve this problem and can quickly converge to atleast a near-optimal solution. Other algorithms, such as successiveinterference cancellation, can be adapted to reduce transmission peaks.

For data transmission with a spreading matrix, such as a CI spreadingmatrix, the transmitting entity may perform spatial processing for eachsubband as follows:

z _(ss) =V·s

where V is a spreading matrix for the subband; and z_(ss) is a vectorwith up to N_(T) spread symbols for the subband. Each data symbol in sis multiplied with a respective column of V to obtain up to N_(T) spreadsymbols.

In general, D data symbols can be sent simultaneously on each subbandwith matrix spreading, where 1≤D≤S. The D data symbols in s may bemultiplied with a N_(T)×D spreading matrix V(k) to obtain N_(T)spatially processed symbols for z_(ss). Each spatially processed symbolfor each subband includes a component of each of the D data symbolsbeing sent on the subband. The N_(T) spatially processed symbols foreach subband are then transmitted on the S spatial channels of H.

In one aspect of the disclosure, wherein D<S, an additional spreadingmatrix is calculated and used to multiply the D data symbols. Theadditional spread data symbols are transmitted on one or more of theremaining S−D spatial subchannels, wherein the additional spreadingmatrix can be calculated to reduce the PAPR of transmissions from one ormore of N_(T) antennas. Alternatively, or in addition to the methodabove, one or more data symbols can be selected to provide PAPRreduction. As stated above, any of various techniques, includingiterative techniques, can be employed to calculate the PAPR-reductionsignals.

FIG. 14 is a flow diagram that depicts the function of the spatialprecoder 1302.1-1302.N according to some aspects of the disclosure.Channel state information (CSI) for the RAN downlink is input 1401 forcalculating the eigenmodes 1402. At least some of the eigenmodes areselected for transmission 1403. A spatial precoding matrix is calculated1404 and used to precode 1405 user data streams for transmission.

It should be appreciated that some of the steps depicted in FIG. 14 canbe combined. One or more transmitters can be selected for PAPR reduction1412. For example, the antenna array might comprise one or moretransceivers with power constraints. Thus, the one or more transceiversmight be selected in order to improve their power efficiency. One ormore eigenmodes are selected for PAPR reduction 1413. Processes 1403 and1413 can be performed concurrently. Based on the eigenmodes selected forPAPR reduction, the precoding matrix may be adapted 1414. The precodingmatrix is generated based on both the eigenmodes providing for userdownlink channels and the eigenmode(s) providing for PAPR reduction.Thus processes 1404 and 1414 can be combined. Precoding data 1405 cancomprise precoding user data streams, any control information, and thePAPR-reduction signals. Selecting the PAPR-reduction signals 1415 cancomprise an iterative procedure whereby the PAPR-reduction signals areadapted relative to each user-data block in order to achieve somePAPR-reduction metric. For example, the metric might comprise athreshold PAPR for each of the selected transmitters, a PAPR averageacross the selected transmitters, or a minimum PAPR achieved from apredetermined number of iterations or during a predetermined processinginterval. Other PAPR-reduction metrics might be employed.

The various blocks shown in the figures may be viewed as method steps,and/or as operations that result from operation of computer programcode, and/or as a plurality of coupled logic circuit elementsconstructed to carry out the associated function(s).

In general, the various exemplary aspects may be implemented in hardwareor special purpose circuits, software, logic or any combination thereof.For example, some aspects may be implemented in hardware, while otheraspects may he implemented in firmware or software which may be executedby a controller, microprocessor or other computing device, although theinvention is not limited thereto. While various aspects of the exemplaryembodiments of this disclosure may be illustrated and described as blockdiagrams, flow charts, or using some other pictorial representation, itis well understood that these blocks, apparatus, systems, techniques ormethods described herein may be implemented in, as non-limitingexamples, hardware, software, firmware, special purpose circuits orlogic, general purpose hardware or controller or other computingdevices, or some combination thereof.

It should thus be appreciated that at least some aspects of theexemplary aspects of the disclosure may be practiced in variouscomponents such as integrated circuit chips and modules, and that theexemplary aspects of this disclosure may be realized in an apparatusthat is embodied as an integrated circuit. The integrated circuit, orcircuits, may comprise circuitry (as well as possibly firmware) forembodying at least one or more of a data processor or data processors, adigital signal processor or processors, baseband circuitry and radiofrequency circuitry that are configurable so as to operate in accordancewith the exemplary aspects of this disclosure.

Various modifications and adaptations to the foregoing exemplary aspectsof this disclosure may become apparent to those skilled in the relevantarts in view of the foregoing description, when read in conjunction withthe accompanying drawings. However, any and all modifications will stillfall within the scope of the non-limiting and exemplary aspects of thisdisclosure.

1. An apparatus, comprising: a code-division multiplexer configured tomultiplex each of a plurality of data streams into a different one of aplurality of spread-Discrete Fourier Transform (DFT) code divisionmultiple-access channels; a DFT spreader configured to spreadmultiplexed original data symbols to produce a plurality of DFT-spreaddata symbols; a mapper configured to map each one of the plurality ofDFT-spread data symbols to one of a plurality of Orthogonal FrequencyDivision Multiplexing (OFDM) subcarriers; and an inverse discreteFourier transform (IDFT) configured to generate an OFDM transmissionsignal comprising the plurality of OFDM subcarriers, each modulated withone of the plurality of spread data symbols.
 2. The apparatus of claim1, wherein the code-division multiplexer is configured to arrange theoriginal data symbols in each of a plurality of length-N blocks to bespread by the DFT spreader, such that each of the plurality of datastreams is spread with a code set corresponding to its spread-DFT codedivision multiple access channel.
 3. The apparatus of claim 1, whereinthe DFT spreader comprises the code-division multiplexer.
 4. Theapparatus of claim 1, further comprising a scheduler communicativelycoupled to the code-division multiplexer and configured to assign eachspread-DFT code division multiple access channel to one of a pluralityof User Equipments (UEs).
 5. The apparatus of claim 1, wherein the DFTspreader employs at least one of a set of orthogonal codes and a set ofquasi-orthogonal codes to spread the multiplexed original data symbols.6. The apparatus of claim 1, wherein the OFDM transmission signalcomprises a sequence of single-carrier frequency division multipleaccess (SC-FDMA) symbols, each SC-FDMA symbol comprising a plurality ofcode-division multiple-access channels.
 7. The apparatus of claim 1,wherein the mapper maps the plurality of DFT-spread data symbols tocontiguous or non-contiguous OFDM subcarriers.
 8. The apparatus of claim1, further comprising a scheduler configured to assign multiple ones ofthe plurality of data streams to a common Physical Resource Block (PRB)based on at least one of similarity in modulation scheme and similarityin scaling factor.
 9. The apparatus of claim 8, further comprising alayer mapper configured to map each PRB to at least one of a differentlayer and a different power amplifier.
 10. A method, comprising:multiplexing each of a plurality of data streams into a different one ofa plurality of spread-Discrete Fourier Transform (DFT) code divisionmultiple-access channels; spreading multiplexed original data symbols toproduce a plurality of DFT-spread data symbols; mapping each one of theplurality of DFT-spread data symbols to one of a plurality of OrthogonalFrequency Division Multiplexing (OFDM) subcarriers; and operating aninverse discrete Fourier transform (IDFT) on the DFT-spread data symbolsto generate an OFDM transmission signal.
 11. The method of claim 10,wherein each of the plurality of DFT-spread data symbols is asingle-carrier frequency division multiple access (SC-FDMA) symbolcomprising a plurality of sub-symbols that comprises the original datasymbols code-division multiplexed into the plurality of spread-DFT codedivision multiple-access channels.
 12. The method of claim 10, whereinthe multiplexing arranges the original data symbols in each of aplurality of length-N blocks for spreading, such that each of theplurality of data streams is spread with a code set corresponding to itsspread-DFT code division multiple access channel.
 13. The method ofclaim 10, wherein the OFDM transmission signal is a downlink signal. 14.The method of claim 10, wherein the multiplexing further comprisesassigning each spread-DFT code division multiple access channel to oneof a plurality of User Equipments (UEs).
 15. The method of claim 10,wherein the spreading employs at least one of a set of orthogonal codesand a set of quasi-orthogonal codes to spread the multiplexed originaldata symbols.
 16. The method of claim 10, wherein the OFDM transmissionsignal comprises a sequence of single-carrier frequency divisionmultiple access (SC-FDMA) symbols, each SC-FDMA symbol comprisingoriginal data symbols multiplexed to a plurality of code-divisionmultiple-access channels.
 17. The method of claim 10, wherein themapping is configured to map the plurality of DFT-spread data symbols tocontiguous or non-contiguous OFDM subcarriers.
 18. The method of claim10, further comprising assigning multiple ones of the plurality of datastreams to a common Physical Resource Block (PRB) based on at least oneof similarity in modulation scheme and similarity in scaling factor. 19.The method of claim 19, further comprising mapping each PRB to at leastone of a different layer and a different power amplifier.
 20. AnOrthogonal Frequency Division Multiplexing (OFDM) transmitter apparatusconfigured to generate an OFDM multiple-access signal with lowPeak-to-Average Power, the transmitter apparatus comprising at least oneprocessor, at least one memory in electronic communication with the atleast one processor, and instructions stored in the at least one memory,the instructions executable by the at least one processor to: multiplexeach of a plurality of data streams into a different one of a pluralityof spread-Discrete Fourier Transform (DFT) code division multiple-accesschannels; spread multiplexed original data symbols to produce aplurality of DFT-spread data symbols; map each one of the plurality ofDFT-spread data symbols to one of a plurality of OFDM subcarriers; andperform an inverse discrete Fourier transform (IDFT) on the DFT-spreaddata symbols to generate an OFDM transmission signal.
 21. The apparatusof claim 20, wherein the instructions to multiplex provide for arrangingthe original data symbols in each of a plurality of length-N blocks forspreading, such that each of the plurality of data streams is spreadwith a code set corresponding to its spread-DFT code division multipleaccess channel.
 22. The apparatus of claim 20, wherein the instructionsto multiplex provide for assigning each spread-DFT code divisionmultiple access channel to one of a plurality of User Equipments (UEs).23. The apparatus of claim 20, wherein the instructions to spreadprovide for employing at least one of a set of orthogonal codes and aset of quasi-orthogonal codes to spread the multiplexed original datasymbols.
 24. The apparatus of claim 20, wherein the OFDM transmissionsignal comprises a sequence of single-carrier frequency divisionmultiple access (SC-FDMA) symbols, each SC-FDMA symbol comprisingoriginal data symbols multiplexed to a plurality of code-divisionmultiple-access channels.
 25. The apparatus of claim 20, wherein theinstructions to map provides for mapping the plurality of DFT-spreaddata symbols to contiguous or non-contiguous OFDM subcarriers.
 26. Theapparatus of claim 20, further comprising instructions to assignmultiple ones of the plurality of data streams to a common PhysicalResource Block (PRB) based on at least one of similarity in modulationscheme and similarity in scaling factor.
 27. The apparatus of claim 26,further comprising instructions to map each PRB to at least one of adifferent layer and a different power amplifier.